Talk:Black hole/Archive 13

Black hole simulation improvement request (11th December 2010)

Thank you for this great article, it is very informative.

Please consider improving the black hole simulation so that the light gets attracted to the black hole. In the current simulation the light seems to get repelled away from the black hole. This is a bit confusing.

Or kindly explain why the light swells when it approaches the black hole.

Thank you.

Albertatambo (talk) 08:49, 11 December 2010 (UTC)

The simulation looks correct to me. Here is an illustration of why this leads to magnification: http://www.spacetelescope.org/static/archives/images/screen/heic0814f.jpg Amaurea (talk) 17:51, 16 December 2010 (UTC)

I don't see how scientists have evidence to back up their conclusion with black holes, if they have never been able to get close enough to actually study them then how do they know they're real? i mean it could always be a colapsed star or unknown galisky.. who knows? ~Ashley —Preceding unsigned comment added by 68.56.145.145 (talk) 00:46, 20 January 2011 (UTC)

Edit request (21 January 2011)

"This temperature decreases with the mass of the black hole, making it difficult to observe this radiation for black holes of stellar mass." I put in a Citation needed tag for this and it was deleted. According to Leonard Susskind's book, "The Black Hole War..." temperature decreases as mass increases - the wording above makes it sound as if temperature decreases as mass decreases. This should be clarified and should include a proper citation. Later in the article it is stated with a citation that temperature is "proportional to" mass, but again, doesn't specify the direction of the proportion.

Doooook (talk) 01:37, 22 January 2011 (UTC)

Well, proportional means by definition that as one increases the other increases and vice versa. In the main article it correctly says that the temperature is proportional to the surface gravity, which is inversely proportion for mass. To prevent any possible confusion it even clarifies that this means that large black holes emit less radiation than small black holes. I don't see how there is any room for confusion there.

On the other hand I see how the statement in the lead can be misinterpreted. I'll have a go at clarifying it.TR 10:09, 22 January 2011 (UTC)

Edit request from Jofo2005, 29 January 2011

{{edit semi-protected}} |ref=harv}}</ref> which were shown to be rapidly rotating neutron stars by 1969.

Done Next time, please state what you want changed more clearly (like, "please add the word were in the sentence..."). It makes it easier to tell what change needs to be made. Qwyrxian (talk) 06:03, 30 January 2011 (UTC)

Please clarify text in the article

The following text appears in the article, but I think it could be clarified:

In 1915, Albert Einstein developed his theory of general relativity, having earlier shown that gravity does influence light's motion. Though, a few months later, Karl Schwarzschild gave the solution for the gravitational field of a point mass and a spherical mass.

I think the text needs to explain (in a little more detail) the relevance of general relativity to the topic and what "solution" Schwarzschild was providing. Also unclear is the meaning of the "Though"? Is this meant to be a contrast of some sort? (Yes I more or less understand the physics; my concern is with what is being communicated.) Thanks!—RJH (talk) 22:59, 31 January 2011 (UTC)

It's probably worth spending a bit of time digging through the edit history, as this feels like a vestige from a past editing dispute. There should be a clearer version of that passage in there somewhere. --Christopher Thomas (talk) 23:24, 31 January 2011 (UTC)

I'm not sure how that sentence came about. I've changed it to "Only a few months later, ...". That makes at least some sense.TR 09:03, 1 February 2011 (UTC)

Concerning black holes' existence

I have read in the top of this discussion page that some user (unfortunately he/or she didn't signed the post) proposed to add explicitly in an statement the until-now hipothetical existence of black holes.

This seems to be an recurring issue here. As a matter of fact, this is an recurring issue in the physics community.

What this user received as a reply was:

... Also, it is unnecessary since the statement "a black hole is a region of space" does not say if such a region exists. The set of such regions in reality could be empty. ...

I think this is not a valid answer. I never assigned to Phylosophy 101, but I think that the set of things endowed with the attribute of being cannot be empty. So the statement "a black hole is a region of space" asserts that black holes do exist and they are a region of space.

I'm not trying to lecture no one here, but the thing is: people from inside the community are used to this question about the existence of black holes, but outsiders don't. And since astronomers are still searching for "That" ultimate evidence (the one they can call a "proof"), the existence of such objects must be considered hypothetical.

Why can't this be explicitly stated in this article? IMHO this is 'a must' to stand for a NPOV.

Cheers. Seneika (talk) 22:55, 28 January 2011 (UTC)

Please provide a high quality, reliable, academic source that states what you are proposing. Jehochman ^Talk 01:41, 29 January 2011 (UTC)

Surely I can. But can you be more specific? To what part of what I've said are you refering? Depending on it, I can cite every text book on general relativity or else I can cite books and papers related to astronomy. You see, I'm not talking of that part of the story regarded as fringe science. I'm talking simply of the state of art in relativity and astronomy. Seneika (talk) 10:53, 29 January 2011 (UTC)

You have to come up with a qualified source that states that black holes are considered hypothetical. You may find that this is not as easy as you would think. Dauto (talk) 03:00, 30 January 2011 (UTC)

In what follows I present a list of quotations accompanied by the sources. These are explicit references to endorse what I have proposed.

This first one is for historical purposes

"... these exotic objects remained a textbook curiosity until 1960's..."

Here we have it explicitly stated

"Testing the black hole hypothesis"

"Black holes are theoretical structures in spacetime predicted by the theory of general relativity"

and here several other quotations

"Observations of the binary X-ray source Cygnus X-1 in the early 1970's provided the first plausible evidence that black holes might actually exist in space."

"Do black holes exist?"

"...Evidence now suggests that black holes do exist"

"... the goal of confirming the detailed predictions of general relativity for their geometries is still for the future."

This is a good final one

"Although there is no conclusive evidence available for the existence of blackholes at the moment, presently the best candidates seem to be the binary stars in which one of the partners is visible and the other is supposed to be a blackhole."

I want to reiterate that my only intention is to put to the reader's eyes that the conception of black holes began as purely theoretical but now the scientists affirm to have strong reasons to belive that black holes do in fact exist. Nevertheless, there's no final conclusion on the subject, and this is a work in progress.

To my understanding, all this is implied in the article and may now be explicitly stated.

Cheers --Seneika (talk) 03:58, 1 February 2011 (UTC)

My references

The current first sentence makes absolutely no statement about the existence of black holes, it merely what a black hole is. There is no assertion (or even implication) of existence in that sentence. On the other hand, inserting the word "hypothetical", as the anon ip suggested, has the strong connotation that no such objects are thought to exist. Such as statement would thereby violate NPOV, as there is a significant portion of the community (especially within astrophysics) that believes that the existence of black holes is sufficiently proven. (For example by the absence of hard X-ray emissions for soft X-ray transients with masses above the TOV limit while in quiescence.)

The position of the community cannot (and thereby should not) summarized in a single word in the first sentence. The correct place in the lead to discuss this would be last paragraph that summarizes the observational evidence. This paragraph can do with some tweaking anyway. (In my opinion at least, it overemphasizes Sag A*, as compared to the emphasis given in the main article.) In tweak should be wary of WP:SYNTH however. (ie. no conclusion should be drawn, which cannot be directly attributed to a source).TR 09:32, 1 February 2011 (UTC)

I agree with you. Except for your first two sentences. When one reads

A 'black hole' is a region of space from which nothing, not even light, can escape.

one finds the existence of such objects to be implied, since it's being described without any reference to its nature. As a matter of fact, not all properties of black holes being described in the whole first paragraph are known observed (or observable) facts. These are theoretical predictions. If black holes and all its refered properties were observational facts then attributing to them some theoretical nature would be nonsense. But on the contrary, most of what is 'known' about black holes is found in the form of theoretical prediction. It would be different, for example, if one were talking about antiparticles, whose nature moved from theoretical to physical reality long ago.

I agree that in many cases a sentence like

A 'black hole' is a hypothetical region of space from which nothing, not even light, can escape.

comes in the form of an attempt to stablish one's own point of view (or even to demerit the research in this field). I am not supporting here the edition of that sentence to this form. On the other hand a sentence like

According to the general theory of relativity, a 'black hole' is a region of space from which nothing, not even light, can escape.^{[reference here]}

seems to be appropriate. The third paragraph could start with

Although there's no ultimate proof (or evidence) for the existence of black holes, astronomers have identified numerous stellar black hole candidates...^{[references to this statement here]}

In the way I'm proposing it, I don't think it would fall in WP:SYNTH or even WP:OR and would certainly satisfy WP:NPOV. --Seneika (talk) 13:09, 1 February 2011 (UTC)

The problem with a sentence like

According to the general theory of relativity, a black hole is a region of space from which nothing, not even light, can escape.^{[reference here]}

is that this definition of a black hole is independent of general relativity. Within any description of spacetime, a region which is not in the causal past of future timelike infinity (aka region from which nothing can escape) would be called a black hole. This exactly the reason that the "according to general relativity" phrase was removed in the past.

Some different variant may be needed. I'm not averse to adding some reference to general relativity to the first paragraph. In fact, I think it should be mentioned somewhere in the lead.

As for the sentence,

Although there's no ultimate proof (or evidence) for the existence of black holes, astronomers have identified numerous stellar black hole candidates...^{[references to this statement here]}

This might be too strong, since there is certainly a part of the community that would maintain that the ultimate proof has already been delivered. Considering this, such a sentence may actually violate NPOV.TR 13:55, 1 February 2011 (UTC)

But history tells us that a scenary where astronomers started to identify interesting black regions on space and developed the concept of a region of space from which nothing, not even light, can escape. is not the case. The way you put it, for example, the notion of a black hole would imply at least in the notion of spacetime. You see, these definitions are not paradigm-independent. Even the primordial idealization of a black hole, that of an object whose superficial gravity is so strong that even light cannot scape, implies in a theory for gravity. Many (I can't be sure if all of them) observational techniques to detect black holes are embued in the paradigm of such theory. It happens that our currently theory for gravity also dictates our notion of spacetime and it is general relativity. So why is a sentence beginning with "According to GR..." not appropriate? I think it would not only be appropriate, but also accurate. This whole article is written in an "According to GR..." style, BTW.--Seneika (talk) 16:12, 1 February 2011 (UTC)

First of all, starting with "According to GR..." implies that in other theories a black hole may be something different. In particular it suggests that the notion of a black hole has an existence independent of "an region of space which things may enter but not leave". In that sense it actually might have to opposite effect of what you are trying to achieve.

Secondly, the description of a black hole given in the first sentence is applicable to a whole slew of theories; not just GR, but also supergravity, f(R)-gravity, Hořava-Lifshitz gravity, causal sets, etc. Basically in any modern (alternative) theory of gravity A black hole is a region of space from which nothing, not even light, can escape. Not only is it applicable to such theories, but black hole solutions in such theories are actively studied (as one can see from looking at recent articles on the gr-qc ArXiv). Of course, the article further focuses on the properties of black holes as predicted by GR (although many (like hakwing radiation and gravitational red shift) are in fact independent of GR. GR is after all the currently accepted best model for gravity.TR 09:43, 2 February 2011 (UTC)

Regarding my second proposal of edit, that sentence can be modified in many ways. Take for example

Although the existence of an ultimate proof (or evidence) for the existence of black holes is not consensual, astronomers have identified numerous stellar black hole candidates...^{[references to this statement here]}

Isn't that accurate? Why mentioning this would be a violation of WP:NPOV? The lack of references to sources attesting the contrary wouldn't also be a problem? Otherwise just one side of the story will be told. IMHO, there is a difference between the assurance of neutrality in POV and the absence of POVs. One may say that this article lacks NPOV (or at least accuracy) by omission. The referencies I cite above present to the reader the current state of observations and of the understanding of the phenomenon (in a neutral manner, for what I could see). I'm not citing any controversial sources, just reviews found in journals like 'Nature' or 'Scientific American' and also known textbooks.

Just to finalize, I want to emphasize my opinion that somewere in this article this must be told (a bit on the lead and perhaps more in a subsection). --Seneika (talk) 16:12, 1 February 2011 (UTC)

To first respond to your final remark, I would like to draw your attention to the Observational evidence section, which IMO gives a fairly accurate summary of the observational status of black holes. In particular the black hole#Alternatives subsection gives a discussion the various reason why one might think that the current evidence is not enough.

However, talking about an "ultimate proof" is nonsense. An "ultimate proof" rarely (if ever) exists in science. Implying that it should be given is therefore misleading.TR 09:43, 2 February 2011 (UTC)

Improving the lead

Per WP:LEAD the lead section should summarize the main points of the article, reflecting the emphasis on those points given in the main text. As it currently is, the lead has the following issues with this:

• The history section is not covered in any way.
• Nothing is said about the formation and evolution of black holes.
• The lead currently spends two paragraphs on observations. In particular the evidence for the supermassive black hole at Sag A* is discussed in too much detail and thereby overemphasized.
• No mention is made of general relativity.

Remedying these points may also help alleviate the concerns of user:seneika raised above. I think the best way forward is to merge the current second and third paragraph about observational evidence and cut down on the detail. We then have space to add a paragraph on the history and a paragraph on the formation. Does this sound like a plan? TR 09:58, 2 February 2011 (UTC)

Suggestion for the first paragraph

I suggest changing the first paragraph to (something like):

A black hole is a region of space from which nothing, not even light, can escape. The theory of general relativity predicts that a very compact mass will deform the spacetime around it to form such a region. Around a black hole there is an undetectable surface called an event horizon that marks the point of no return. It is called "black" because it absorbs all the light that hits the horizon, reflecting nothing, just like a perfect black body in thermodynamics. Quantum mechanics predicts that black holes also emit radiation like a black body with a finite temperature. This temperature is inversely proportional to the mass of the black hole, making it difficult to observe this radiation for black holes of stellar mass.

The main change is to the second sentence, which now explicitly states that black holes are a prediction of general relativity.TR 11:02, 4 February 2011 (UTC)

suggestion for merger of second and third paragraph

I would like to suggest to following as a merger of the current second and third paragraph:

Despite its invisible interior, the presence of a black hole can be inferred through its interaction with other matter. Astronomers have identified numerous stellar black hole candidates in binary systems, by studying its interaction with its companion star. Moreover, there is growing consensus that supermassive black holes exist in the centers of most galaxies. In particular, there is strong evidence of a black hole of more than 4 million solar masses at the center of our Milky Way.

Maybe accretion discs should be mentioned more clearly?TR 11:02, 4 February 2011 (UTC)

Suggestion for a paragraph about history

This is a very rough draft for a paragraph summarizing the main points of the history section:

Objects whose gravity field is too strong for light to escape were first considered in the 18th century by John Michell and Pierre-Simon Laplace. The first modern prediction of a black hole in general relativity was found by Karl Schwarzschild in 1916, although its black hole nature was not fully realized for another 4 decades. For a long time black holes were considered a theoretical curiosity. This changed in the 1960s when theoretical work showed that black holes were a generic prediction of general relativity, and the discovery of neutron stars sparked interest gravitationally collapsed compact objects as a possible astrophysical reality.

Should it alos mention the work on gravitational collapse by Chandrashekar and TOV in 1930s?TR 11:02, 4 February 2011 (UTC)

suggestion for a paragraph about formation

The following is a suggestion about a blurb about the formation and evolution of BHs.

Black holes of stellar mass are expected to form when heavy stars collapse in a supernova at the end of their life cycle. After a black hole has formed it can continue to grow by absorbing mass from its surroundings. By absorbing other stars and merging with other black holes, supermassive black holes of millions of solar masses may be formed.

This is very rough. I'm not even sure if having a separate paragraph is necessary. I do however feel it is necessary to make the connection supernova->black hole, since that is something a wide audience may have heard about.TR 11:02, 4 February 2011 (UTC)

IP comment

The section on singularities could use the addition of this new article: http://io9.com/5596712/every-black-hole-may-hold-a-hidden-universe The scientist in the article describes a theory in which the singularity predicted by classic GR is not what happens at the center of the black hole. Sorry if I have done something wrong, the semi-protection of non-controversial pages has forced me to the talk page which I have never used before. Thanks. —Preceding unsigned comment added by 76.121.148.242 (talk) 07:26, 23 November 2010 (UTC)

That article is baloney. If there’s a universe inside a singularity, then that universe contains black holes, which contain universes, which contain black holes, etc, etc.

More interestingly, and amazingly, in 15 years there could be direct observational evidence of what is going on inside a black hole. See: http://arxiv.org/pdf/1011.5874

Briefly, this is what its about: Its estimated a few supermassive black hole mergers occur per year, in the center of merging galaxies. These mergers are preceded by about a month with a unique electromagnetic signature which along with the Laser Interferometer Space Antenna (LISA) can identify the host galaxy. Then the physical merger of these SMBHs will take seconds depending on size. If black holes are point singularities, at the merger nothing will be ejected of course. If black holes contain a distributed mass (perhaps a radiation star), a massive ejection or gamma ray burst will occur. 172.131.133.144 (talk) 01:26, 30 December 2010 (UTC)172.129.62.38 (talk) 16:48, 4 January 2011 (UTC)BG

Radiation ejection from supermassive black hole core mergers might not be possible due to a large (Schwarzchild radius)/(core radius) ratio, and the merger of smaller black hole cores could be much better candidates for radiation ejection. Estimates are a few potentially observable smaller black hole mergers occur annually, so this should be observable in our lifetimes. 172.163.67.59 (talk) 14:51, 6 February 2011 (UTC)BG

Other suggestions

It seems to me that sections 2,3 and 5 are affine. They're all about theory of black holes. I think merging them into a major section called 'Theory' would be nice. The usage of subsubsections may not be a bad idea. Take for example this (featured) article about acetic acid.

My suggestion is to structure the article in the form

• History

• Theory: current sections 2,3 and 5 and perhaps a subsection entitled 'concurrent theories'

• Observation: the current section 4 plus a section entitled 'Missions' (or a more appropriate title)

This 'concurrent theories' subsections may be a good idea to tell a little about of how other theories handle the concept of black holes. (Alternative theories is not really my expertise, so I think I couldn't contribute here for the moment, although I think they worth being mentioned)

In this 'Missions' subsection I'm proposing one would list projects related and/or dedicated to BH observation. As well as other sources of BH detection.

There's no mention to gravitational waves in the article. Was it decided to be kept that way?

Cheers. --Seneika (talk) 13:08, 2 February 2011 (UTC)

Could you elaborate what you think is the added value of this reorganization?

As for gravitational waves, I'm not sure what you want to mention about them. Since, no gravitational waves have been detected to date, they do not provide any real additional data on black holes. As for black hole mergers as a source of gravitational waves, that seems to be a subject better covered in the gravitational wave article.

As for further expansion with a "missions" section. The article already is fairly long, so I'm hesitant for further expansion. It may be worth while to consider if such discussions are better off in stellar black hole, X-ray binary or supermassive black hole, since missions typically try to observe a very specific class of objects.TR 14:47, 2 February 2011 (UTC)

I think a reorganization (not necessarily the one I've proposed) would help to make the article cleaner. Separating more clearly theory from observational fact. (Don't you agree that section 4.6 is kind of misplaced?)

Many theoretical aspects are used to explain what is observed about BHs, (many) other aspects, however, are (highly theoretical) predictions. IMHO this could be separated in a more logical way since little of what one reads in sections 2 and 3 are observational facts (although these are indeed facts about BHs). The structure of a BH fits better in 'theory'. The same is valid for 'Open questions'. Most of these topics are better discussed in their own respective articles.

You seem to be concerned in adding here only 'real additional' information about BHs. From this POV I can't attest the relevance of GWs. It was just a suggestion. (But it seems that in the near future gravitational radiation will most likely to be detected than thermal radiation from black holes, for example. Oscilatory normal modes of BHs is an active field of research that can lead to BHs 'finger prints').

In this same philosophy one can't attest the 'practical' relevance of any of those results arising from the semi-classical approaches (quantum evaporation, for example), yet these are found in this article (for the sake of completeness, I imagine).

About this 'missions' section it could be as little as a paragraph (smaller, for example, than section 5). Just a few comments about common sources of data on BHs.

In sum I think a reorganization would add the value of sections more clearly separated by their nature (history, theory and observation) resulting in a cleaner article.

Please don't interpret me as some one just arriving here with parachutes and saying whatever I want. I'm just pointing things I think could improve the article and, what is more important, I'm offering myself to do things, not just saying people to do it.

--Seneika (talk) 16:47, 2 February 2011 (UTC)

I actually think that the organization of the article is pretty clear. (Of course, I am biased in that respect, since I'm responsible for a lot of the current organization.) The first section provides a clear context of the subject by discussing its history. The second answers the "What", what is a black hole and what are its properties. The third answer the "How" and "When" questions; How and under what conditions do black holes originate. The fourth section section then explains what observational evidence exists for black holes. Section 4.6 is very much in its place, since it highlights the various caveats of the observational evidence. The last section then discusses several topics of current research. By nature, this discussions will be more technical than the previous sections, a best practice for technical articles is to have the most technical sections as last. This helps with the general accessibility.

About gravitational waves, as it stands the possibility of detecting anything using GWs is based on a lot of wishful thinking, given that no GWs have been detected to date. As such any speculation on what might be learned using GWs seems more in its place in the article on GWs and GW detectors. Once detection of GWs has become a reality, which might be soon, it might also be time to have a blurb here.TR 17:11, 2 February 2011 (UTC)

Despite my opinion that this is something that can't be, I thought at first that this article were intended to be relied mainly in 'astrophysical BHs'. I got this idea first reading the lead, were there's no reference to any theory (and by any I mean 'GR', since it's the only one reliably theory on the subject, according to the mainstream of Physics) ruling the definitions and concepts being proposed; and later our discussion confirmed that idea.

In practice, however, this article deals with a wide range of aspects regarding BHs. Not just what is observed and I agree this would be an impossibility, since most of the subject is highly theoretical.

In fact, most of these topics are strongly hypothetical. Take, for example, the case of the gravitational singularity inside a BH, whose existence or not is a matter of debate that extrapolates the realm of astronomy or astrophysics, since observation would be impossible by definition. Other examples range from inter-universe travel, to quantum evaporation (or vice-versa). These are examples of topics often appearing when one talks of BHs. In the present article this is no different, they're are here as well.

In this article it appears to be room left for topics not of only hypothetical nature but also especulative. This is easily seen in a sentence like

A phase of free quarks at high density might allow the existence of dense quark stars,[107] and some supersymmetric models predict the existence of Q stars.[108] Some extensions of the standard model posit the existence of preons as fundamental building blocks of quarks and leptons which could hypothetically form preon stars.[109]

Supersymetric models or anything outside the standard model is controversial isn't it? This is an example of a highly especulative subject appearing in the present article. Not to mention 'the possibility of travelling to another universe'.

Not that I want to advocate in favor of GWs, but when you say

Once detection of GWs has become a reality, which might be soon, it might also be time to have a blurb here.

I must ask why 'supersymetric models', 'extensions of the standard models' and even predictions of semi-classical approaches have a blurb here without having become 'reality' first. Did the level of 'wishful thinking' related to them garantee that? Isn't it a little arbitrage?

When one talks about the structure and evolution of BHs, I think it must be in a different tone of that when one speaks of the structure and evolution of the sun, for example.

Although the structure and evolution of 'ordinary' stars are also theory, represented in models, the high number of independent evidences attesting such models in this case allows one to talk about the structure of these stars without explicitly and repeatedly saying that this is theory. The same doesn't apply in the case of BHs. When you say that

The second answers the "What", what is a black hole and what are its properties.

it can't be left unclear that 'its properties' do not reffer necessarily to observed properties of BHs. As many of such properties are simply not observable and some are even hypothetical, it's not clear what is this 'what' being answered. For this reason I still suggest the existence of the section entitled 'Theory' with what is now section 2 being a subsection of it.

I'm not sure about what question is subsection 3.4 answering. (What 'when'?)

The whole of subsection 4.6 relies in highly especulative subjects. I'm still not convinced that it is in it's right place. There's already section 5 for 'Open questions'.

Off course, all this annoyance of mine stops making sense when one admits this article as a portal to whatever is related to BHs. But this is also not clear. --Seneika (talk) 22:57, 3 February 2011 (UTC)

The article tries to cover all aspects of BHs. Since most of what has been written about BHs is of theoretical nature, a lot of the article is concerned with theoretical aspects. (The lead at this point does not reflect this very accurately, which is why I started the section above to improve it.) In fact, the only section concerned with observation is the section called "observational evidence". The current section 4.6 completes the discussion of the observational evidence by relating what the possible alternative explanations are for the observed BH candidates. Part of the point is that any such explanation would require exotic speculative physics. The place of this section is in the "observational evidence" section, since it is about alternative explanations of the evidence, not about alternatives of black holes.

Obviously, the subject is very broad, which is why many of the (sub)sections have been written in WP:SUMMARYSTYLE, and refer to a main article for more detail.

I'm still not quite clear on what you want to say about GWs in this article. As far as I know, most discussion about BHs and GWs has been in the context of BH mergers as a possibly detectable source of GWs. This is a subject which is much more about GWs than Bhs (for example, if there were other similarly heavy compact objects, their merger would be just as interesting), and is thereby more suited for the GW article. As far as I know, there has been little to no (serious) discussion about using GWs to learn about BHs (unlike for example in cosmology, where you can find quite extensive discussions about what the GW background could teach us if we could the detect it). I could however be wrong about this. If there is documented discussion of this in secondary sources (review papers, textbooks, etc.) this would indeed warrant a short discussion in the "observational evidence" section.

I do agree that the article could make it clearer that black holes are a theoretical phenomenon for which we are searching for empirical verification, rather than an empirical phenomenon for which one searches for a theoretical explanation. Improving the lead could help with this.TR 10:03, 4 February 2011 (UTC)

I really don't know much about the aspects on which GW and BH subjects cross over each other. The little I know is found in reviews like (apparently this is already found in some textbooks). The picture is like this (I'll omit all the IFs I think should be in what follows, but assume for the moment that GWs and BHs do exist and are those predicted by GR. I'll be short because I know little and to respect the not-a-forum policy)

GWs may arrive to Earth comming from the more remote sources. Regardless their origin, GWs can be scattered by BWs. The interaction between GW and BH will cause the last to oscilate. The (quasinormal) modes of oscilation of the BH will be imprinted in the outgoing GW. Different BHs will have different modes of oscilation, scattering GW in their own peculiar way. This is belived (wished, hoped...) to provide a way (presumably the only possible way) to probe the presence of BHs directly.

AFAIK, the merger scenary presents a good candidate for detection of GWs. This scenary of scattering of GWs by BHs would present a probe for the presence of BHs. (Off course, GWs must then be assumed to exist). This is why I thought the subject to deserve a comment in this article (and because this seems to be a field of research in activity since the 70's relying in predictions of GR about BHs). Perhaps in section 4.6 then. Seneika (talk) 14:00, 5 February 2011 (UTC)

My references — Preceding unsigned comment added by Seneika (talk • contribs) 00:41, 6 February 2011 (UTC)

Note: this ref. to Davies isn't mine. I haven't manage to fix this... Seneika (talk) 00:48, 6 February 2011 (UTC)

It appears that there is enough information for a short subsection about the prospects of detecting BHs using gravitational waves, similar to the short subsection about detecting strong gravitational lensing by BHs, one or maybe two paragraphs long. I do not really have time to delve into this right now, so do you maybe feel like drafting a suggestion for such a section?TR 11:48, 6 February 2011 (UTC)

Sure. I can do that until the end of the week. Seneika (talk) 13:02, 8 February 2011 (UTC)

Edit Request (15th Feb 2011)

{{Edit semi-protected}}

The word "the" has been duplicated in the General Relativity section of the article.

http://en.wikipedia.org/wiki/Black_hole#General_relativity

"[...] to produce the the solution describing [...]"

 Done - DVdm (talk) 13:51, 15 February 2011 (UTC)

Main Image

The artist's rendering at the top of the page could lead people to believe they're purely fictional bodies. I'm thinking if we use a double-stacked image instead, showing both the rendering of a black hole alone In space and an actual image from NASA of a galaxy with a central black hole. I'd suggest the recent image of NGC-4649 from the Chandra X-Ray Observatory.

--Ben Harkness (talk) 18:54, 25 February 2011 (UTC)

I think having multiple images in the lead would look messy, especially on small displays. It might be a good image for the observational evidence section, which could do with more actually telescope pictures and less artists impressions.TR 21:01, 25 February 2011 (UTC)

Citation standards

This article was recently edited with an edit summary beginning "Spaced initials"; spaces were inserted in initials in the references, for example, "Davies, P.C.W." was changed to "Davies, P. C. W." Spacing of initials was then undone with an edit summary "restore unspace version per WP:CITEVAR".

This is not what WP:CITEVAR is about. WP:CITEVAR says "Do not change the citation style used in an article merely for personal preference or cosmetic reasons." The issue here is "citation style." Citation style refers to a standard way of listing a citation. This article stores all of its references in {{cite}} templates, so Wikipedia automatically determines the citation style. Citation style is concerned with the precise order of various elements including author, journal name, page, publication date, and city; which of these elements take punctuation including periods, commas, quotation marks, colons, and parentheses; and whether authors' names are last name first or first name first.

Citation style is distinct from general usage style, which is concerned with issues such as the en dash (–) for page range, and how initials are spaced. If an article were created with all of its page ranges expressed with hyphens, WP:CITEVAR does not prevent changing those hyphens to en dashes, because such a change is a matter of general usage style, not citation style. Similarly, spacing initials is a matter of general usage style, not citation style. The Wikipedia style standard is spaced initials, as can be seen by these examples: J.R.R. Tolkien redirects to J. R. R. Tolkien; George H.W. Bush redirects to George H. W. Bush; D.W. Griffith redirects to D. W. Griffith; I.M. Pei redirects to I. M. Pei. Spaced initials of human names is standard. For example, The Chicago Manual of Style 14th edition says in section 7.6 on page 237:

Names and initials of persons are capitalized:

...

R. W. B. Lewis

...

The space between initials should be the same as the space between initial and name (not R. W.B. Lewis), except when initial are used alone, without periods (see 14.4).

Spaces in initials is standard throughout Wikipedia and Standard English. In fact, the articles referenced in this article are published in journals that use spaced initials. For example, reference [1] is to an article in Reports on Progress in Physics, which uses spaced initials without periods; reference [13] is to an article in Physics Today, which uses spaced initials with periods; reference [15] is to an article in Physical Review, which uses spaced initials with periods; reference [17] is to an article in Nature, which uses spaced initials with periods.

In sum, WP:CITEVAR says not to change established citation style within an article, but spacing of initials is an element of general usage style, not citation style, and as such, usage errors in the spacing of initials can and should be corrected. —Anomalocaris (talk) 23:53, 2 March 2011 (UTC)

Spaces in initials is very much a citation styles. Names can be presented several ways. John Michael Smith / Smith, John Michael / John M. Smith / Smith, John M. / J. M. Smith / J.M. Smith / JM Smith / Smith, J. M. / Smith, J.M. / Smith, JM / Smith JM, and possibly others. Headbomb {talk / contribs / physics / books} 04:58, 3 March 2011 (UTC)

Well, if you look at the bibliography in Carroll 2004 you will see that this uses unspaced initials. The same goes for 50% of the other books that are currently sitting on my desk. This disproves your assertion that spaced initials in references are a universal standard. Hence WP:CITEVAR applies. Case closed.TR 09:19, 3 March 2011 (UTC)

Edit request from Raza536, 3 March 2011

{{edit semi-protected}}

respected sir/Madam, I have some concepts of black hole which i want to share with every one so please allow me to edit the page to post my view point thak you Raza536 (talk) 06:45, 3 March 2011 (UTC) Raza536 (talk) 06:45, 3 March 2011 (UTC)

You would need to suggest specific edits. Jehochman ^Talk 11:27, 3 March 2011 (UTC)

Per WP:NOR, this is also probably not the best place to try to present your own ideas about black holes. The Wikipedia article is supposed to focus on information that's already been published in sources that meet the guidelines given in WP:RS (in this case, academic literature). --Christopher Thomas (talk) 19:05, 3 March 2011 (UTC)

Properties and structure

Extended content

Maybe WP isn't the place to pose such a question, but the article states that "a charged black hole repels other like charges just like any other charged object." [emphasis added] However, according to the Standard Model of particle physics electric charge is mediated by virtual photons. Given that nothing can escape the pull of a black hole, how can a charged black hole propagate an electric field? Curvature of charge-space?! Any pointers would be greatly appreciated. :) nagualdesign (talk) 00:22, 3 March 2011 (UTC) WP indeed isn't the place to ask this question. The picture of forces in the standard model being mediated by virtual particles shouldn't be taken to literally. It is a graphic way of systematizing the terms in the perturbation expansion, nothing more. The word virtual in virtual particle means that the particle doesn't obey the (classical) equation of motion. In particular, a virtual particle can "move" a speeds greater than the speed of light. This is not an issue because virtual particles weren't physical to begin with. (e.g. they also do not need to conserve energy). The electric field of a charged black hole is static, hence nothing is propagating anywhere. More intuitively. Electric charges respond to the retarded potential. In the case of a cloud of charged matter collapsing to a black hole, charges outside the black hole will see the matter as frozen at the horizon and respond to that.TR 09:33, 3 March 2011 (UTC) Thanks for the feedback, Tim. Lot's of good food for thought there. And I apologize for 1. - I'll try to maintain my contribution/question ratio at a higher level in future. :) nagualdesign (talk) 00:56, 6 March 2011 (UTC)

(above section collapsed by nagualdesign (talk) 23:33, 16 March 2011 (UTC). Please do not delete it.)

Random observations

Here are some random observations in the nature of a partial review. Hopefully these may be of some small use to the primary editors of this article.—RJH (talk)

• "...although its black hole nature..." I think the meaning of this statement needs to be explained for the reader because it is vague.

  I agree, this phrasing is not optimal. It is meant to convey the fact that although, the Schwarzschild solution was found the in 1916, it took until 1958 for someone to give this the physical interpretation of what we now call a black hole, as is detailed in the history section. If you have an idea for a better phrasing, please have a go.TR 10:08, 17 March 2011 (UTC)

  Perhaps "...although the physical details of this model were not fully understood for another four decades."?—RJH (talk)

  I've tweaked the sentence a bit. Is that better?TR 09:01, 30 March 2011 (UTC)

  Sorry, the new wording kind of has the same issue.RJH (talk)

  Would it help if "black hole" in the offending sentence would be replaced "region of space from which nothing can escape"?TR 08:19, 4 April 2011 (UTC)

Based upon Crothers (2006) pp. 55–56, Schwarzschild found the solution of Einstein's field equations for a point mass in a vacuum. Crothers says that the mathematical description for a black hole was actually independently completed by Kruskal and Szekeres in 1960. He contradicts the claim that Schwarzschild predicted black holes.—RJH (talk)

Note that Progress in Physics is not exactly an WP:RS. The author, Crothers, is a known crackpot, who does not seem to understand the concept of coordinate change and coordinate independence. Anyway, what is true, is that Schwarzschild did not interpret his solution of the Einstein equations as a black hole. The singular nature of that solution, was subject of much discussion. It is not until the 1950s, and the introduction of the concept of an event horizon, that this solution got the interpretation of describing a region of space that one could enter, but cannot be escaped. (A concept that later would be called a black hole.) This is conveyed in some detail in the history section. This single sentence in the lead should convey this in some condensed form.

I'm starting to think that the problem is not the last part of the sentence, but the first part. I'll do some tweaking, please see if that helps.TR 08:13, 18 April 2011 (UTC)

• Regarding the sentence: "This is different from other field theories like electromagnetism, which does not have any friction or resistivity at the microscopic level, because they are time-reversible." This sentence jumps between the use of plural and singular, leaving some ambiguity. Is the macroscopic-level sub-sentence talking about the theories or electromagnetism? If the latter, why does the end of the sentence jump back to plural?

  Should have been plural.  FixedTR 10:08, 17 March 2011 (UTC)

• Why does the article need a section on the "Photon sphere"? It seems to add little value.

  It is an interesting feature of black holes (although it is not restricted to black holes). More importantly it has a very direct effect on the appearance of a black hole. The black disk shown in the simulated view of BH in the lead, actually is the photon sphere, not the horizon. (Because any light ray passing through the photon sphere is captured by the BH.) Maybe this could be made more clear? Anyway, I don't see much harm in having the section.TR 10:08, 17 March 2011 (UTC)

• Per the "Formation and evolution" section, it is possible that supermassive black holes formed directly from direct gas inflow without the need for one or more seed black holes.[1] Does this need to be mentioned?

  Probably, not yet sure where though.TR 10:08, 17 March 2011 (UTC)

• I think the entire section "Observational evidence" could be substantially tightened up by eliminating tangential information and compacting the summaries.

  Did you have anything specific in mind? Giving it a quickly look, I don't see many point that could be significantly tightened without loss of relevant information, except may be the galactic nuclei subsection.TR 10:08, 17 March 2011 (UTC)

  • I'm not clear (from the wording) that GRBs provide "observational evidence" of black holes as such. They do provide evidence of collisions or gravitational collapse, which could result in a black hole. Hence, this part seems to belong in the "Formation and evolution" section.—RJH (talk)

    I think the article could do without the section GRBs altogether. It is more a subject for the GRB article than this one. Here it doesn't really add anything.TR 09:01, 30 March 2011 (UTC)

  • In the "Galactic nuclei" section, I think it should more strongly suggest that the SMBH are responsible for the AGN. Otherwise, the activity wouldn't necessarily provide observational evidence.—RJH (talk)

    I'll have a go at sharpening the wording later.TR 09:01, 30 March 2011 (UTC)

  • The "Alternatives" section doesn't seem to discuss observational evidence. Possibly it should be moved to the Open questions section?—RJH (talk)

    The "Alternatives" section discusses alternative explanations for the presented observation evidence, which is why it is in that section. It does two things, on one hand it shows why current evidence is not completely conclusive. On the other hand it shows which physical principles/assumptions you would need to give up in order for the current evidence not to prove that black holes exist.TR 09:01, 30 March 2011 (UTC)

• The article is inconsistent about the use of "a black hole" vs. "the black hole". If it is talking about, say, "the black hole event horizon", then I think "the" makes sense. Otherwise, as there are many black holes, most of the time it should probably say "a black hole" or "the black holes".

  I'll have a look.TR 10:08, 17 March 2011 (UTC)

• "...it is best to free fall the rest of the way." Why is it "best"? Quicker death?

  Best to maximize the time it takes to hit the singularity. Not sure why there is a source of confusion, considering the first half of that sentence.TR 10:08, 17 March 2011 (UTC)

  "They can prolong the experience by accelerating away to slow their descent, but only up to a point; after attaining a certain ideal velocity, it is best to free fall the rest of the way." As I read it, this is saying that, below the ideal velocity (which remains undefined), constant acceleration away from the singularity shortens the duration until the observer reaches the singularity (in the observer's reference frame, presumably). At first glance this seems counter-intuitive; is this another relativity-based paradox?—RJH (talk)

  This is indeed paradoxical. It is related to the fact that a timelike geodesic is a path that maximizes the proper time between two events, i.e. free falling clocks tick faster than other clocks. This leads to a common statement that, to prolong once stay in a black hole before hitting the singularity, one should just free fall all the way. There is a subtlety, however. The singularity is not one point in space time, it is a line of points, and it matters at which point on the line you hit the singularity. For an observer entering the black hole at a certain time there is an optimal (from the perspective of maximizing life expectancy) point to hit the singularity. To maximize your lifetime you should follow a timelike geodesic (free fall) to this point. (If think this coincides with entering the black hole at zero radial velocity.) Observers entering the black hole at any other velocity should try to change their velocity to get closer to the ideal one as fast as possible. The longer they wait the further away from the ideal trajectory they will end up (with a different ideal final velocity.) The ideal velocity therefore depends on the initial velocity a ship has as it enters the BH and the maximum thrust it can produce. (Which why it is not really possible to mention what the ideal velocity is.

  As you can see this a somewhat lengthy explanation, which is why it isn't in the article. A reader interested in the details can look up the reference, which is fairly readable.TR 09:01, 30 March 2011 (UTC)

Thank you.—RJH (talk) 19:20, 16 March 2011 (UTC)

No, thank you for taking the time.TR 10:08, 17 March 2011 (UTC)

But Something Does Escape

The first sentence claims that nothing can escape from a black hole. Five sentences or so later, I read that black holes emit radiation. Oops.192.249.47.195 (talk) 16:27, 28 March 2011 (UTC)

The radiation comes from outside the blackhole. Dauto (talk) 19:25, 18 April 2011 (UTC)

Obviously that can't be correct, as the paragraph on Evaporation explains that the emitted radiation results in a mass loss from the black hole according to E = mc2.192.249.47.195 (talk) 16:37, 20 April 2011 (UTC)

Looks reasonable to me. Do you have a source which says that mass loss through evaporation is incompatible with some other key part of the theory? bobrayner (talk) 16:50, 20 April 2011 (UTC)

We seem to have gotten off-subject here. The article contains the claim that "nothing can escape from a black hole". It then goes on to explain that there is a small amount of electromagnetic radiation that all black holes emit. Thus, something does indeed escape from a black hole and the claim that nothing does is false.192.249.47.195 (talk) 17:00, 20 April 2011 (UTC)

Objects that fall into the hole are forever lost, and never seen again. In that sense, nothing ever escapes. Black holes can create certain types of radiation - Hawking radiation, and (if you choose to express them in terms of virtual particles) electrostatic and graviational fields. You can think of these as being created just outside the horizon, or you can think of them as resulting from virtual particles (which, unlike everything else, are allowed to travel faster than light), or you can think of the black hole as being one big particle and the created radiation being "tunnelling" of that particle from one state to another (much as with particle decay). No matter how you choose to look at it, it's fundamentally not "escape" in the normal sense of the term. --19:23, 20 April 2011 (UTC)

Certainly you can't be serious. You have just presented an incredibly convoluted argument to justify a simply fallacy. Maybe physicists have their own dictionary. Here are the first two definitions of escape:

 To break loose from confinement; get free. 
 To issue from confinement or an enclosure; leak or seep out.

Hawking radiation is fundamentally "escape" in the normal sense of the term. I don't think I'm challenging any sacred black hole theory here. I'm just pointing out that the first sentence in the article is wrong. All I'm suggesting is that somebody correct it by possibly adding the phrase "with the exception of Hawking radiation" or something.192.249.47.195 (talk) 19:56, 20 April 2011 (UTC)

No, Hawking radiation is not escape, at least not from the region inside the event horizon. Hawking radiation is the result of quantum fluctuations just outside the event horizon. The same process (effectively) deposits negative energy into the black hole causing its mass to decrease. Anyway, Hawking radiation certainly does not contradict the first sentence defining a black hole as a region of space from which nothing can escape. (That simply IS the definition of a black hole, or rather a translation of the more technical definition to plain English.)TR 20:44, 20 April 2011 (UTC)

Hello? Is anybody out there? This would be humorous if it wasn't so sad. It doesn't take a PhD to recognize that the following two statements contradict each other (both of which are verbatim from the article):

"a black hole is a region of space from which nothing, not even light, can escape." "black holes are not entirely black but emit small amounts of thermal radiation." Would somebody please correct one or the other?192.249.47.196 (talk) 20:04, 21 April 2011 (UTC) ""

Your interpretation differs from that of most scientists, and three different editors here have attempted to explain to you why. If you want to argue about it further, see the big green banner at the top of this page for places where such discussions are on-topic. It is not on-topic here (as this thread is no longer contributing usefully to improving the article). --Christopher Thomas (talk) 21:08, 21 April 2011 (UTC)

I’ve been following this thread with some amusement but felt I must weigh in, as the last post is uncalled for. Clarifying an apparent contradiction would certainly improve the article, would it not? 192.249.47.196 has a legitimate point. The article should summarize how the thermal radiation does not violate the claim that nothing escapes from a black hole. The following candidate sentence from the Hawking radiation article would seem appropriate: “This radiation does not come directly from the black hole itself, but rather is a result of virtual particles being "boosted" by the black hole's gravitation into becoming real particles.”24.151.89.129 (talk) 21:43, 23 April 2011 (UTC)

The reason why I'm shutting down the previous anon is that they moved some time ago from saying "this point needs clarification" to saying "you guys are all wrong about this" in the face of three different attempted explanations. At that point, the thread was no longer useful.

I agree that the subject could stand clarification; if you see a good way to modify the text to accomplish that, by all means go ahead. I considered modifying the lede to mention the points I raised in my first response above, but any change I could think of would have made the lede more confusing.

The reason why I was reluctant to add an explanation involving virtual particles is that virtual particles are a mathematical artifact (of perturbation theory), not necessarily something that actually reflects what's going on. Expressing the problem in terms of virtual particles leads to useful conclusions (energy debt from a virtual particle reduces the hole's mass during Hawking radiation, FTL virtual particles mediate the hole's electrostatic and gravitational fields), but there are equally valid ways of describing the system that don't involve virtual particles (the math just tends to be intractable for any but the simplest of cases). I'd like to hear from some of the GR types lurking here before changing it myself (though by all means be bold if you think you've found a good way of phrasing a useful change). --Christopher Thomas (talk) 22:22, 23 April 2011 (UTC)

Black Hole???

"A black hole is a region of space from which nothing, not even light, can escape. The theory of general relativity predicts that a sufficiently compact mass will deform spacetime to form a black hole. Around a black hole there is an undetectable surface called an event horizon that marks the point of no return. "

In your statement According to you blackhole is a region from where nothing can pass??? m I right??? Well black hole can effect such things which have mass only And by E=mc^2 And law of conversation of energy every energy formly don't have any mass like in case of mass if light can not escape through it then light might be stored in it then it should blast like superNova as energy potential should be filled??? which would lead to formation of new galaxy??? so So the word "nothing" should be replaced by almost nothing as no body can provide accurate information??? And about event horiozon similarly where there is point of entry there always is point of return of exist like in wormhole??? Since light is captured there so the term "undetectable" should be deleted?Thank YouRaza536 (talk) 10:43, 26 April 2011 (UTC)

Edit requests

> Edit required - Paragraph 1

The first sentence of the entire article says, >>"A black hole is a region of space from which nothing, not even light, can escape."

3 sentences later it is directly contradicted by this sentence from the same paragraph: >>"Quantum mechanics predicts that black holes emit radiation like a black body with a finite temperature. This temperature is inversely proportional to the mass of the black hole, making it difficult to observe this radiation for black holes of stellar mass or greater."

These two concepts are prima facia contradictory. Neither are sourced. Obviously, for those who know physics the latter is more accurate and precise.

I am anonymous so I have no editing privileges. Someone please clear up this egregious error. I suggest removing any reference to 'from which nothing can escape' and find properly sourced accurate information that describes the processes of a Black Hole to the best of sciences ability. justinepperly.com

>UPDATE...not to belabor the point but today's Astronomy Pic of the Day says " Jets of streaming plasma expelled by the central black hole of a massive spiral galaxy..." http://apod.nasa.gov/apod/ap110531.html

— Preceding unsigned comment added by 184.100.204.72 (talk) 04:52, 31 May 2011 (UTC)

This has already been discussed, at length, in the other threads on this talk page. To sum up, 1) You can either think of Hawking radiation as coming from just outside the horizon, or think of it as being a quantum tunnelling effect, or think of it as involving virtual particles that are allowed to move faster than light; all work mathematically, and none of these involve time-like paths (the paths that normal particles can follow) leaving the hole, and 2) the relativistic jets leaving black holes are material from the accretion disc that was expelled before passing the horizon. I hope this answers your questions. --Christopher Thomas (talk) 06:59, 31 May 2011 (UTC)

> Edit required - #Singularity

Please clarify that the singularity does not have an infinite gravitational force- it is just considered so for the equations. — Preceding unsigned comment added by 78.146.50.196 (talk) 22:25, 4 June 2011 (UTC)

First, please put new comments at the end of the thread, not in the middle or at the beginning. Second, please sign your comment with four tilde marks (~~~~). This is automatically expanded into a signature.

Third, General Relativity _does_ predict force that becomes infinite as one approaches the singularity. GR's model of black holes is expected to be changed whenever we develop a working theory of quantum gravity, but until then (or until someone goes inside a real black hole with measuring equipment), the statement stands. Quantum gravity is mentioned later in the article already. --Christopher Thomas (talk) 23:04, 4 June 2011 (UTC)

General Relativity v. Quantum Mechanics

White Dwarfs and Neutron Stars are described by Quantum Mechanics whereas Black Holes are described by General Relativity. Accorging to GR, a Black Hole is a singularity, i.e., with zero radius and infinite density. This solution is purely mathematical and is out of step with those for smaller collapsed stars. GR describes space-time around a Black Hole but doesn't describe the Black Hole itself. My impression is that a gravitational singularity wouldn't exist in the real universe and is purely a mathematical construct. I don't get this from my reading of the article. Until a "Theory of Everything" linking GR and QM is developed, we really won't know the true nature of a Black Hole. Virgil H. Soule (talk) 17:19, 10 June 2011 (UTC)

White dwarf stars and neutron stars are described by both general relativity and quantum mechanics. They are examples of relativistic degenerate matter. It is (special) relativity that gives them a finite maximum mass (the Chandrasekhar limit and the TOV limit, respecitively). A black hole is what you get when you have an object heavier than the maximum mass that can be supported by any form of degeneracy pressure.

This is already discussed in the article. --Christopher Thomas (talk) 21:09, 10 June 2011 (UTC)

Thanks, missed the point. I get the impression, however, that even some sort of Quantum Gravitation theory might not be adequate to describe what a Black Hole actually is. That aside, I'm struggling with basic assumptions in relativity. It's my understanding that all bodies are assumed to be point masses, in which case, singularity solutions for Black Holes would be trivial. Virgil H. Soule (talk) 18:47, 11 June 2011 (UTC)

Bodies are not assumed to be point masses. General relativity expresses the geometry of spacetime in terms of the stress-energy tensor, which is the energy/mass density, momentum density, and flow of both energy and momentum as a function of position. It is a continuous distribution defined at all points in spacetime (at least, where the equations produce well-defined answers; a gravitational singularity is a point where they don't, though they remain valid everywhere around the singularity).

Further questions really, really should go to a forum somewhere else, per WP:TALK. Wikipedia:Reference desk/Science is an on-wiki location where questions are accepted, if you really don't want to try an external forum. --Christopher Thomas (talk) 03:41, 13 June 2011 (UTC)

Agreed. Say no more.Virgil H. Soule (talk) 19:34, 13 June 2011 (UTC)

Alternative models

Perhaps alternative ways of significant mass influx to galactic BHs should be entertained; such as polar vortex and jet model. See arXiv 0005119 and appendix of SRM at tmmalm.info.67.91.184.187 (talk) 19:47, 11 June 2011 (UTC)

Preprints generally don't satisfy WP:RS. Also see WP:UNDUE. The purpose of Wikipedia's science pages is to summarize knowledge published in appropriate venues, giving space proportional to the degree of impact an idea has had within the scientific community. Early results generally don't belong in Wikipedia. If they make a splash in the scientific community, they'll eventually be added here at a later time. --Christopher Thomas (talk) 03:45, 13 June 2011 (UTC)

Detecting the event horizon

In the first paragraph the event horizon is called undetectable. If something moves across the event horizion it can be observed; therefore, the horizon cannot be undetectable. — Preceding unsigned comment added by 76.97.227.185 (talk) 00:40, 30 June 2011 (UTC)

The moment of crossing is never observed; instead, to a distant observer, the object appears to slow down and flatten as it approaches, getting fainter and redder, until it finally is no longer visible.

The reason "undetectable" was there is that an observer falling into a black hole doesn't have anything unusual happen when they cross the horizon either. It represents the distance within which further travel towards the centre is inevitable, but a freely-falling extended object can still have forward and backward communication between all parts of itself as it crosses (it just end up not being able to relay any of it to the outside world).

Long story short, it's not a physical object or surface, just a boundary where two coordinate systems stop overlapping with each other. I've adjusted the text to make this clearer. --Christopher Thomas (talk) 01:02, 30 June 2011 (UTC)

Can a Black Hole have Planets?

Has the possibility of planets orbiting a Black Hole been considered in the literature? Could bodies of any size exist in close-in circular orbits about a Black Hole or would they be destroyed by tidal forces? I understand that stars have been found on paths consistent with orbits about a gravitational center in our galaxy. I'm asking about Earth-size bodies or even stars in planetary-type orbits about a Black Hole. Virgil H. Soule (talk) 17:19, 10 June 2011 (UTC)

The big green banner at the top of this page lists places where questions like this would get a better response.

Thanks, been there. Not a friendly place. Virgil H. Soule (talk) 18:47, 11 June 2011 (UTC)

The short answer is, planets could orbit a black hole anywhere they could safely orbit an equal-massed star, at least as far as tidal forces are concerned. Roche limit gives the exact distance (for any object, not just black holes). --Christopher Thomas (talk) 21:12, 10 June 2011 (UTC)

Thanks, should have known. Virgil H. Soule (talk) 18:47, 11 June 2011 (UTC)

Does the article answer the question? -- cheers, Michael C. Price ^talk 07:32, 19 June 2011 (UTC)

It's in the "physical properties" section (last sentence of the first paragraph). --Christopher Thomas (talk) 15:41, 19 June 2011 (UTC)

What are black holes made of?

This article does a decent job of describing theoretical objects, based in a well-established theory. The average reader might think from this article that the existence of BH is as well-confirmed as that of atoms, or photons. That's not so ... but noone would know that from this article.
Editors might have a look at the BBC video "Who's Afraid of Black Holes?" In the first part you'll see some well-known experts asked "What are black holes made of?" From their reactions, it's clear that this article needs to reflect the theoretical nature of black holes. Like the Higgs, it ain't necessarily so. Twang (talk) 07:12, 18 June 2011 (UTC)

Did you actually read the article? It has a whole section discussing the current observational status of black holes, including possible alternatives.TR 11:22, 18 June 2011 (UTC)

Oh boy, the 'Can you read' ploy. Why didn't you name which whole section you mean? 'Open questions'? Don't see anything there that makes it clear to the average reader that, as Larry Krauss puts it, there's 'no smoking gun' yet. Brand-new NPR interview In the video, when the experts are asked what BH are made of, they don't know. I'm suggesting that this article make that clear. It's nothing to be ashamed of. Who the hell understands QM? I don't want to argue about it. Maybe an editor will come along who's willing and qualified to make the effort. I think it's wise not to be too dogmatic/fundamentalist about it. There are a lot of loose ends out there these days. Twang (talk) 06:06, 19 June 2011 (UTC)

The structure of black holes as described by general relativity is well-understood. That is what this article primarily describes. Possible extensions are already mentioned (under "alternatives"), with a few additional ones in the "see also" section. The fact that we don't _have_ a complete description of black hole structure is also prominently stated (in the "open questions" section and elsewhere), so it's unclear what exactly you feel is missing.

I'd also like to point out that, per WP:RS (section "scholarship") and WP:V (section "what counts as a reliable source"), articles on scientific topics should be sourced by scientific literature where possible, rather than popular press and television programs (unless those are exceptionally noteworthy). Textbooks and review articles are the usual references quoted, being secondary sources). Long story short, "this TV program said so" is not enough grounds for changing the article. --Christopher Thomas (talk) 06:36, 19 June 2011 (UTC)

I'd think that if I say "the article has a whole section on the observational status" and the article has a section called "observational evidence", that its quite clear I'm referring to that section. You will also note that, that section has a subsection called "alternatives" which discusses alternative explanations of the observational evidence. Also note that I didn't question your ability to read, I questioned whether you actually read the whole article before posting here. Judging from your reaction, you didn't, which makes me tend to ignore you.TR 12:04, 19 June 2011 (UTC)

I just watched four out of the five parts of the BBC video mentioned above ("Who's afraid of black holes"). It seems clear to me that the video presents the case that black holes are a well understood phenomena. That appears to be contrary to the statement which opened this thread. It seems well established in the video that Black Holes are a prediction of GR. It also appears to be well established in the video that researchers have found convincing (and compelling) evidence that black holes physically exist in the universe, and at the center of our very own galaxy. This is not really new news.

Furthermore, it appears that all the information in the video is already contained in this article. This article provides a deeper explanation of black holes than does the video - and that makes sense. I am sure the video is designed to be a brief overview because of the time constraints of doing a one hour show. Personally, I thought the video did a good job. But I have to agree that it is not useful as a source for this particular article when compared to the scientific literature that is available, and the way that this article is already sourced. ---- Steve Quinn (talk) 01:31, 20 June 2011 (UTC)

Well to me I think a Black Hole is another universe within our universe. Explanation: A Supernova is an implosion (inside explosion) and if the star implodes in the inside it is an explosion or "The Big Bang" Theory. So we or our Universe is a Black Hole sucking in Objects from another universe therefore showing another theory of the universe. The Expanding Theory because the universe is expanding but not on its own but by taking objects, from another universe. So by now the first universe should be way gone because the other black holes sucked everything out, But then again I don't know because i'm only 14. — Preceding unsigned comment added by 184.76.141.83 (talk) 11:41, 9 August 2011 (UTC)

Replacement image

In the section for Entropy and thermodynamics we see File:Black Hole Entropy.png, which I would like to replace with However, when I added the image I was reverted with the edit summary "I like the old one better". So this is the discuss part of the BOLD, revert, discuss cycle. I think the image is obviously superior on its face. It's workaday, just a text image, but it looks professional. The current image looks, well, like it was drawn in crayon by someone going through withdrawal. The genesis of this was a help desk post where the image was sought to be replaced because it was "goofy-looking" so I made the other image. So I'm here for some consensus. I hope people will comment on whether we should keep the current or go with the one I created (or do something else entirely).--Fuhghettaboutit (talk) 04:58, 10 July 2011 (UTC)

If you don't like the goofy one, an ordinary math equation would be the logical replacement. Why make a new image? Dicklyon (talk) 05:05, 10 July 2011 (UTC)

Because there doesn't seem to be a way to make $S={\frac {\pi Akc^{3}}{2hG}}$ render at the larger size appropriate for the section the equation is placed in. If there is a fix for that, then I agree that the TeX should just be used.--Fuhghettaboutit (talk) 05:22, 10 July 2011 (UTC)

Why do you want it larger than the standard equation? Dicklyon (talk) 05:23, 10 July 2011 (UTC)

Have you looked at the section? Aesthetically, the proportions would be very off with the small size. Here, this is what it would look like:

$S={\frac {\pi Akc^{3}}{2hG}}\,\!$

The formula for the Bekenstein–Hawking entropy (S) of a black hole. It depends on the area of the black hole (A), the speed of light (c), the Boltzmann constant (k), Newton's constant (G), and the reduced Planck constant (ħ).

I was the one who made the comment on the help desk (see Wikipedia:Help desk/Archives/2011 June 20#Replacing an image with TeX), and then unfortunately I became busy with other things and didn't follow up. I think ideally we would use an ordinary math equation for this, though I agree that the method suggested here to display a TeX formula doesn't fit with the aesthetics of other images. So I would also support the replacement of the current goofy image with Fuhgettaboutit's replacement image (though this replacement image seems to use a bold font, which seems unnecessary to me; I think a regular-weight font would be better). In any case, we need to fix the current problem that the caption does not match the image—the caption refers to the reduced Planck constant, denoted by ħ, while the formula in the image uses ${\frac {\pi }{2h}}$ instead (where h denotes the ordinary Planck constant). This is one reason a standard math equation would be best: it would be easier to make changes to the formula if needed. —Bkell (talk) 07:00, 10 July 2011 (UTC)

And there's probably no good reason to display the equation in a box with a caption. Dicklyon (talk) 07:07, 10 July 2011 (UTC)

I like the current "goofy" version better. The point of having an image in that section is lightening what would otherwise be a "wall of text". The fact that it shows an equation is secondary. Replacing it with a simple typeset equation sort of defeats the purpose. The current image has the aesthetics of an equation scribbled on a white board (which I like, despite detesting white boards in general). I'd rather see the equation be replaced by a better image, than by a typeset equation. If the point were to show the equation we would do it the usual way set in TeX between lines.TR 10:18, 10 July 2011 (UTC)

I prefer the cleaner, bold one in a non-ridiculous font. It is easier to read, and that is honestly what I care about when looking at equations. Wikipedia is supposed to be competitive with professional encyclopedias... don't make it look like a Sophomore in High School wrote it on a whiteboard. Antman -- chat 10:17, 12 July 2011 (UTC)

The goofy version is very difficult for me to read. -- chbarts (talk) 04:47, 18 July 2011 (UTC)

Having a stylized image of an equation in that section was already somewhat of a stretch, but at least served to break the wall of text. Replacing it with a typeset image of an equation doesn't even serve that purpose, in which case it is better to have no image in that section at all.TR 08:05, 18 July 2011 (UTC)

The large typeset equation did break the wall of text adequately, and also served a teaching purpose (presenting selected important information in a way that draws the reader's attention). I disagree with its removal (and favour the typeset version over the script version). --Christopher Thomas (talk) 09:29, 18 July 2011 (UTC)

Misinterpretation of what's happenig within a black hole

"Observers falling into a Schwarzschild black hole (i.e. non-rotating and no charges) cannot avoid being carried into the singularity, once they cross the event horizon. They can prolong the experience by accelerating away to slow their descent, but only up to a point; after attaining a certain ideal velocity, it is best to free fall the rest of the way."

The bolded part is wrong. Since all paths inside a black hole point futureward to the singularity, every acceleration accelerates towards it (as is correctly illustrated in the picture above that paragraph). There is no path "away from the singularity", because all such paths are in the past. It is best to remove that part, or to rephrase it. The last part ("it is best to free fall the rest of the way.") is correct and the only thing which is suitable to extend one's life (though by a few microseconds only for a typical black hole). Gulliveig (talk) 05:07, 26 August 2011 (UTC)

Please read the reference provided with that sentence.TR 06:14, 26 August 2011 (UTC)

I'd thought so too, but on reading the cited reference, it turns out that that only holds for infalling observers who start at rest at the horizon. Observers that fall from farther away (and so are moving when they pass the horizon) gain a small benefit from using rockets to accelerate outwards for part of their trip (after which it starts decreasing proper time again). --Christopher Thomas (talk) 06:15, 26 August 2011 (UTC)

That paper refers to "accelerating outwards." But there isn't any outwards direction, once you crossed the event horizon (by the definition of a block hole, btw), because outwards = past. All lines point inwards and futurewards, and any attempt to go to somewhere else brings you "more in faster", hence only speeds up the final fate. Time allowing, I will find and quote the source. Gulliveig (talk) 06:38, 26 August 2011 (UTC)

That is only true in Schwarzschild coordinates (where the radial direction becomes undefined at the event horizon). In Eddington-Finkelstein coordinates, which the paper uses, "outwards" is always well-defined. There are other coordinate systems, like Kruskal-Szekeres coordinates, that do this too; each system lends itself to certain types of analysis, and all are valid ways of looking at the situation for the regions where the coordinate system is well-defined.

The light-cones do remain pointed inwards, so moving inwards _is_ inevitable; only the observer-measured rate of infalling changes with rocket thrust (getting worse under most conditions, improving under some). That doesn't mean "inwards" and "outwards" cease to be meaningful concepts. --Christopher Thomas (talk) 07:55, 26 August 2011 (UTC)

Many textbooks do contain statements like "the more you struggle the faster you reach the singularity". The is usually backed by the observation that a geodesic maximizes the proper time between to spacetime events. The flaw in that argument (as pointed out by the ref) is that the singularity is not a single point in spacetime, but actually a line. From a single spacetime point there will be a whole family of radial geodesics that hit the singularity at different points, and have different lengths (measured in proper time). This family can be parametrized by the radial velocity of the geodesic at the initial point. In this family there exists an optimal geodesic that maximizes the proper time. (this basically coincides with an observer crossing the horizon at minimal velocity. The optimal strategy for an observer falling into a black hole is to attempt to get on a geodesic as close as possible to the optimal one. This is generally achieved by accelerating "outwards". (i.e. pushing the radial velocity towards the optimal one).TR 09:38, 26 August 2011 (UTC)

To elaborate on the above, when speaking of candidate directions along which one can accelerate, we shouldn't focus on one's future or past light cone. These represent directions in which you can go and directions in which you can see, but not directions in which you can accelerate. Acceleration is a spacelike vector orthogonal to one's velocity.

No matter what coordinates we use, a vector can always be continued along a geodesic ray. Generally, some directions impact the singularity and some don't. It's natural to say that the former point inwards and the latter point outwards. Melchoir (talk) 10:20, 26 August 2011 (UTC)

Optical effects at event horizon and beyond

One fact I keep missing are the optical (and possible temporal) effects observed while falling into a black hole. I don't mean what an outside observer would see, I mean what you yourself are observing while you're falling in. One interesting source is [2] (it's from NASA, so it should be reasonably reliable). Two peculiar occurances, apparently, once you cross the event horizon are that:

• a.) Everything around you within the event horizon would undergo optical distortions, and
• b.) when you look up outside of the hole, at least with rotating black holes you can see the whole universe speed up as you're approaching the singularity (theoretically, from the singularity's POV, the duration of the whole outside universe is infinitely small). Only problem is that the frequency of incoming light from outside the hole also speeds up (blue shift), so that it eventually turns into hard radiation.

Oh, and no matter what type of hole you fall in, beyond the event horizon a kind of "well" will also occur around you so that you'll really feel like falling into a hole, whereas the incoming light of the outside universe will concentrate an increasingly shrinking circle (which optically resembles what you see when falling away from a hole's opening). --79.193.34.87 (talk) 11:46, 28 August 2011 (UTC)

Magnetic moment

What is the magnetic moment of a black hole? -Theanphibian ^{(talk • contribs)} 15:49, 29 August 2011 (UTC)

Please note that wikipedia is WP:NOTAFORUM. I.e. this is not the best place to ask a question.

The short answer is the g-factor (physics) of a black hole is 2.TR 18:05, 29 August 2011 (UTC)

Is it? Doesn't it get quantum corrections like the gyromagnetic factor of an electron? — Preceding unsigned comment added by Dauto (talk • contribs) on 18:09, 29 August 2011 (UTC)

Well, I thought it would be a notable fact for the article, which is missing. Wouldn't it come from the basic parameters like mass, charge, and angular momentum? Maybe you would also apply the g-factor to that? Right now I seem to be thinking that it would be 1/2 Q L / M -Theanphibian ^{(talk • contribs)} 20:22, 29 August 2011 (UTC) -Theanphibian ^{(talk • contribs)} 20:22, 29 August 2011 (UTC)

If what TR said above is correct the equation would be $\mu ={\frac {QL}{M}}.$ I would expect quatum corrections to apply though. Dauto (talk) 02:05, 30 August 2011 (UTC)

There might very well be quantum corrections, but they would depend on the theory of quantum gravity employed. I'm not sure there is even any literature on that. I'll try to see if I can find some references for the classical g-factor of a black hole.TR 05:58, 30 August 2011 (UTC)

I don't have time to really do anything with this but the following seem to be the relevant (primary) references

• Carter, B. (1968). "Global Structure of the Kerr Family of Gravitational Fields". Physical Review. 174 (5): 1559. Bibcode:1968PhRv..174.1559C. doi:10.1103/PhysRev.174.1559.
• Cohen, J.; Tiomno, J.; Wald, R. (1973). "Gyromagnetic Ratio of a Massive Body". Physical Review D. 7 (4): 998. Bibcode:1973PhRvD...7..998C. doi:10.1103/PhysRevD.7.998.
• Wald, R. (1974). "Black hole in a uniform magnetic field". Physical Review D. 10 (6): 1680. Bibcode:1974PhRvD..10.1680W. doi:10.1103/PhysRevD.10.1680.

I'd would be good to have a more recent decent secondary source (review article or textbook) that discusses this in more detail.TR 08:46, 30 August 2011 (UTC)

Those references agree with your statement. Here's a quote from the second ref. "we obtain g→2 (the same value as for an electron)." Now, it is known that the electron receives quantum corrections to its g-factor which are independent from its mass so it shouldn't be surprising if a blackhole's g-factor also got corrected. After all, a black hole can be seen as a fundamental particle. Dauto (talk) 13:35, 30 August 2011 (UTC)

Can it? Really? (a black hole be seen as a fundamental particle. This is not what explicit models such as fuzzballs are saying.) But yes, it is very likely that the magnetic moment of a black hole will be corrected by a theory of quantum gravity. It this point however it is pretty much impossible to tell what they would be.TR 20:30, 30 August 2011 (UTC)

Yes, if the no hair theorem applies, then a black hole is described by only three properties -> mass, charge, and angular momentum. That means it has no internal structure (no hair) making it a fundamental object. Keep in mind that the no hair theorem is likely only approximately valid since a black hole's entropy is finite. I don't think this kind of calculation is completely outside of the sphere of currently solvable problems. Dauto (talk) 02:06, 31 August 2011 (UTC)

So it seems like the magnetic moment would be $\mu =g{\frac {QL}{M}}.$ with the stipulation that physicists might not be sure what g is, although generally it's 2-ish, maybe more. -Theanphibian ^{(talk • contribs)} 18:45, 2 September 2011 (UTC)

The correct formula is $\mu =g{\frac {QL}{2M}}.$ where g is two-ish. Dauto (talk) 00:13, 3 September 2011 (UTC)

Alternative black hole models

There is some big misconception about the fuzzball proposal for black holes: A fuzzball is not an alternativ model but a (possible) gravitational description of a black hole microstate among lots of other candidates already known from the dual conformal field theory correspondence. Such a microstate has to be horizonless otherwise it could not explain the large entopy which is related to the black hole. Coarse graining of the exp(S) (here S is the Bekenstein entropy) black hole microstates yields a singular metric [1][2]. As no physical observer with exp(-S) resolution exists (maybe not even in principle) [3], the question of a horizonless and regular 'fuzzball' is irrelevant for any physical observer or infalling probe. Please edit the relevant parts in the article.

References:

[1] http://adsabs.harvard.edu/cgi-bin/bib_query?arXiv:0811.0263 [2] http://adsabs.harvard.edu/cgi-bin/bib_query?arXiv:hep-th/0508023 [3] http://adsabs.harvard.edu/cgi-bin/bib_query?arXiv:1102.3566 — Preceding unsigned comment added by 93.129.166.199 (talk) 22:37, 13 September 2011 (UTC)

"Alternative" in this context means "something other than a GR-plus-Hawking-radiation-alone" model. By describing the microstate, and especially by removing the horizon, fuzzball models are indeed alternatives to this baseline model. --Christopher Thomas (talk) 23:35, 13 September 2011 (UTC)

Maybe it is a question of physical interpretation and definition. But for all physical observers not having the required resolution to infer differences between the ordinary classical concept and the new one, these differences are completely irrelevant. The only difference between a fuzzball model and a classical black hole is that infalling probes might tunnel into microstates before reaching the singularity, which itself has to emerge as a coarse grained effective singularity. But this strongly depends on the tunneling rate and is not know at the moment (but see http://adsabs.harvard.edu/cgi-bin/bib_query?arXiv:0808.2096). Moreover do you understand what exp(-S) resolution means? And there is nothing special with the fuzzball models. Since Bekenstein it was known that a consistent QG needs to account for the exp(S) black hole microstates, which by definition have to be horizonless, otherwise the problem of black hole entropy would become even harder to solve...

So I think it is very important that readers understand fuzzballs not as alternative black hole models but only as the microscopical realizations of their states. In addition to that the most successful new physical theories do not get away with older ones, but implement them as special cases. Or do you believe that a human can't be a human because his individual atoms are governed by the abstract laws of quantum physics which have nothing in common with our daily life experience? — Preceding unsigned comment added by 131.220.96.32 (talk) 12:57, 14 September 2011 (UTC)

But nonetheless, even as a statistical ensemble a fuzzball will never be a black hole according to the classical definition, simply because eventually things do get out, scramble beyond recognition no doubt, but they do get out. As such it does not satisfy the definition of a region of space(time) from which nothing can escape.

Anyway, the main point you seem to be making, that to a classical observer there is (almost) no detectable difference between a fuzzball resolved black hole and a classical black hole, is (IMHO) clearly stated in the article.TR 13:37, 14 September 2011 (UTC)

Another alternative model. Count Iblis (talk) 18:16, 14 September 2011 (UTC)

Reply to the article: The statement "(and can thus not really be considered to be a black hole)" could be misleading because one should not compare the physical properties of a single black hole microstate with the properties of the whole black hole spacetime which consists of exp(S) microstates. Please remove the bracket. I think most people will otherwise not see the difference.

Second: It would be more precise to replace "distant observer" by classical or semiclassical observer. — Preceding unsigned comment added by 93.129.68.169 (talk) 22:16, 14 September 2011 (UTC)

To the Vachaspati Paper: The authors used Schwarzschild coordinates which by definition do not allow to study/follow matter crossing the event horizon in finite time. The drawn conclusions are therefore an artifact of an insufficient choice of the coordinates.

No, see e.g. Section 7, page ten and further. Count Iblis (talk)

No it would mean that a black hole would evaporate within an infall timescale of GM/c^3~20s for SgrA*. See therefore http://adsabs.harvard.edu/cgi-bin/bib_query?arXiv:0806.0628 ... — Preceding unsigned comment added by 131.220.96.32 (talk) 09:42, 15 September 2011 (UTC)